Fosamprenavir calcium is chemically the calcium salt of (3S)-tetrahydrofuran-3-yl-(1S,2R)-3-[[(4-aminophenyl)sulfonyl](isobutyl)amino]-1-benzyl-2-(phosphono oxy)propyl carbamate of Formula I:

Fosamprenavir calcium is a prodrug of amprenavir, an inhibitor of HIV protease, and is indicated in combination with other antiretroviral agents for the treatment of human immunodeficiency virus (HIV-1) infection.
U.S. Pat. No. 6,436,989 provides a process for the preparation of sodium salt of fosamprenavir which involves treating fosamprenavir with aqueous sodium bicarbonate, isolating the sodium salt of fosamprenavir by a resin column and lyophilization.
U.S. Pat. No. 6,514,953 provides processes for the preparation of fosamprenavir which includes hydrogenating (3S)-tetrahydrofuran-3-yl[(2S,3R)-4-{(2-methylpropyl)[(4-nitrophenyl)sulfonyl]amino}-1-phenyl-3-(phosphonooxy)butan-2-yl]carbamate of Formula II
using palladium-carbon in the presence of sodium bicarbonate or sodium hydroxide, water and industrial methylated spirit. After hydrogenation, the reaction mixture is filtered to remove the catalyst and the filtrate is treated with aqueous solution of calcium acetate to obtain fosamprenavir calcium.